Colloquia

Samenvatting

Additive manufacturing (AM) opens up new worlds of design freedom, enabling the rapid and mould-free production of complex parts for a range of industries including the aerospace industry. Laser powder bed fusion (L-PBF) is an AM process capable of manufacturing complex-shaped parts by melting metallic powder using a laser, in a layer by layer fashion, directly from a CAD (Computer-aided design) model. In recent years the field of AM employing L-PBF has advanced rapidly. The quality of the produced parts are approaching the level required by the aerospace industry, mainly through advances in process control and process monitoring. Hence, the emphasis on the development of the L-PBF process may change from process control to microstructure control.

In this research project the relation between the process conditions, the developed microstructure and the (mechanical) properties of a complex-shaped aerospace part have been investigated employing Inconel 718, which is a well-known creep resistant, weldable and corrosion resistant nickel-based superalloy. The influence of different geometrical features (i.e. overhangs, thin or thick sections and complex shapes) on the microstructure and (mechanical) properties was studied. Also, the influence of a post-manufacturing heat treatment on the resulting microstructure and (mechanical) properties was included.

The as-built parts showed an inhomogeneous dendritic microstructure comprising in general columnar grains oriented mostly parallel to the build direction. The grains extend through multiple as-deposited layers due to epitaxial growth. The differences in local process conditions led to variations in the mechanical properties of the different geometrical features as observed through hardness measurements. After the post-manufacturing heat treatment a considerable increase in the hardness of 33 % on average was observed. Moreover, the variations in hardness of the different geometrical features were also removed yielding a part with almost uniform mechanical properties. Apparently, the post-manufacturing heat treatment is not only a powerful treatment to enhance the mechanical properties, but also to remove inhomogeneities in the mechanical properties that are almost inevitable during manufacturing of products with complex features.